Air Conditioning Problem Troubleshooting Page

This page contains some Air Conditioning problems and parts that in use to repair the problems. These problems occur most often every summer. You can repair your air conditioner and save money!
Listed below are many of the air conditioning problems that happen on a daily basis. I wanted to list some of the problems and give you a chance to purchase the parts, and repair your air conditioner yourself.
Please always, make sure all electrical power is turned off before attempting to do any heating or air conditioning repairs.

Problem #1: Outdoor condensing fan motor has stopped running

This problem could be caused by a bad motor run capacitor. If your motor capacitor is not the problem, then more than likely you need a new motor. Is the fan blade tight, stiff or hard to turn? If the fan blade is hard to turn then you probably need a new motor.

Problem #2: Air conditioner compressor will not start

When power is applied to the air conditioning outdoor unit the fan starts, but you hear a sound like the compressor is trying to start, "UGGG"..., for about 5 to 10 seconds and then all you hear is the outdoor condenser fan run. The compressor is locked and will not start. What is happening is the compressor is trying to start, but because the compressor motor is locked it tries to start for a few seconds and then because of the high amperage being drawn goes off on internal overload. The internal overload protects the compressor windings from overheating and burning up. Some compressors just have a hard time starting after sitting all winter long. Some compressors are locked up so bad that you need a new compressor or new air conditioning system. Many times it’s possible to get the compressor started again without having to buy a new compressor or new air conditioning system by using the device "Super-Boost."
The Super-Boost could save you from having to purchase a new air conditioning compressor or system!
The Supco, Super-Boost has the following features that make it a life saver when it comes to air conditioning repair:
The Supco can save stuck compressor by increasing the compressor's starting torque by 500%.
  

The Supco, Super-Boost is a solid state relay and hard start capacitor no loose parts or complicated wiring. Just wire it across your run capacitor as shown below.

On dual capacitor systems just connect between the "C" and "Herm" terminals. See picture above.

More Features:
The Super-Boost can be used on all PSC single phase 115 volt thru 288 volt air conditioning units from 4,000 to 120,000 BTU.
It can be used on a wide range of air conditioning compressors from 4,000 BTU window units to 10 ton commercial units.
The Supco Super Boost is used for tight or locked compressors, if you have low voltage, or for quick recycling of the compressor.

Problem #3: The problem is a bad compressor or fan run capacitor

The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run. You checked and reset your breaker and the outdoor unit still does not come on. You can hear a little humming sound, sometimes an "Uggg" inside the unit when power is applied. The "Uggg" is the compressor trying to start. You might hear the low voltage contactor humming. You should pull the disconnect and disconnect the power to your outdoor air conditioning unit. Make sure your electrical power is off before working on any air conditioning equipment. You take the door or cover off your outdoor unit's control box and find a bad, swollen run capacitor. EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB's. Since they stopped allowing the use of PCB's the capacitors now have a shelf life. Sometimes you need a special meter to test the microfarad (MFD) rating. Most of the time you can tell the capacitor is bad because it is swollen up. See the picture for the comparison between a good and bad dual run capacitor. They call them, "Dual" because the capacitor helps run both the fan and the compressor.
     
Bad round dual capacitor on the left. Bad oval capacitor on the left.
Solution: You need to purchase a new capacitor.

Problem #4: Air Conditioning outdoor condensing unit or heat pump unit will not shut off

It continues to run no matter what you do. The only way you can get the outdoor unit to shut off is turn off the breaker or pull the outdoor disconnect. Also, sometimes when the contactor fails the outdoor condensing unit will not come on at all. Dirt or insects can get in between the contact points while the contactor is off, and cause the air conditioner not to come on at all. When the contactor is stuck in the "On" position (contacts welded together), Ice will form on the indoor evaporator coil and all the way out to the outdoor unit. There could be up to 2 inches of ice form on the line set and outdoor unit compressor. You will not get hardly any air flow through your duct work when this happens because the evaporator has become a complete block of ice. If this is your problem then your contactor points could be stuck, welded together causing the outdoor unit to run continuously. Many times when ants or insects get between the contactor points the outdoor unit will run (burns the insect out), but because of the uneven wear (arcing) in the contact points the contactor will soon fail. Arcing causes a tremendous heat build up and pitting of the contact points. If you are in an area of the country where insects are prominent in and around air conditionings, then I would suggest you blow your contactor out with compressed air or check and make sure you do not have any insects in between the contactor points at the beginning of each cooling season. You might want to keep a spare contactor on hand.
If your contactor looks like the single pole contactor, with burnt or pitted contacts then you need a new contactor. On the picture is a single pole contactor out of a Rheem air conditioner.

Solution: You need to solve this problem by purchasing a new contactor.
Contactor's Purpose: The contactor has a 24 volt relay, when this 24 volt relay is energized from the thermostat, a call for cooling, the contacts on the contactor close, making a high voltage (220-240) connection to your compressor and outdoor fan, causing the outdoor unit to come on. There are several types of contactors.
Make sure your electrical power is off before attempting to remove or work on air conditioning equipment. Before changing out a contactor or working on an air conditioner make sure you pull the outdoor disconnect or indoor breaker that controls the air conditioner. Turn the furnace off or thermostat off so no low voltage is going through the low voltage wiring.

Term-Lok Compressor Terminal Repair Kit Model TLC-3-10:

Problem #5: Compressor will not run

Problem #6: Nothing works on your heating & air conditioning system. The fan will not blow in the fan "ON" position. The gas burners will not light; the outdoor air conditioning unit will not come on.

Solution: Use a Volt Ohm meter, set the meter to "Volts AC," to check and see if you are getting between 24-28 volts between your "C" and "R" terminals on your low voltage board, or between "R" the red low voltage thermostat wire and ground. You might have to tape the blower door safety switch, to keep the voltage on so you can perform this test. Turn your power back OFF after completing this test using the Volt meter. Check for fuses on the furnace control board to see if the furnace has a low voltage protection fuse. If the furnace has a fuse, pull the fuse out and see if it is blown. If the fuse is blown check all your low voltage wiring to make sure it is not grounding out anywhere. It can be pinched wires that are stuck between furnace doors, animals that have chewed through wires and just weathered low voltage wiring that has lost its insulation due to the hot sun. Any wires that are touching together can cause the low voltage fuse to blow. The fuse protects the expensive furnace control board from getting burned up because of a short to ground. If the fuse is blown then you should go to the local hardware and purchase 5 to 6 new fuses. If you do not find the problem that is causing the fuse to blow right away then you will need more than one fuse for testing. If your fuse is OK or your furnace does not have a fuse, and you are not getting low voltage between the "C" and "R" terminals then you might need a low voltage transformer. Some of the transformers just go bad.
What is a Low Voltage Transformer? The job of a low voltage transformer is to take 110 volts AC on the primary end, and transform or lower the voltage to 24 volts on the secondary end. That is why on the transformer label, below it has "PRI" 120, 208, 240 and SEC 24V 40VA. The transformer can be used with multiple voltages either 120 volts, 208 volts or 240 volts. You would hook up the right color coded wire to use the voltage that you have. The color coded voltage wiring directions are on top of the transformer. For example: The white and black wires would be used for 120 volts for most furnaces. The White and Orange wire would be hooked up if you were using the transformer to replace a bad transformer on an outdoor air conditioner or heat pump that uses 240 volts.

International Refrigeration Products Low Voltage Universal Transformer Model TFM4031

Problem # 7: You might consider purchasing and installing the following device if:

1. You have to reset your air conditioning circuit breaker often.
2. If you have electrical storms where the power is going off and on.
3. If the power goes off and on often in your home. If the power goes of and on often in your home then this can ruin a compressor. When your air conditioner is turned off you should wait at least 3 to 5 minutes before you turn it back on. If you do not wait the 3 to 5 minutes then this causes a tremendous strain on the compressor motor because the motor is trying to start without the pressures being equalized. Give your compressor and air conditioning system time for the pressures to equalize before starting your air conditioner again.

Solution: Purchase a delay on make timer. You can set this timer to the length of time you want to wait for the air conditioner to come back on from .03 of a second to 10 minutes. What this timer does is delay the amount of time you want your air conditioner to come on when low voltage power is applied to the timer. This low voltage timer is simple to install. *Some of the new thermostats have this delay feature built into them. If you have a thermostat that has this delay feature, then you do not need to purchase the Delay on Make Timer. If you want to protect your air conditioning system from short cycling and possible compressor damage, then the Delay on Make timer is for you! Remember to turn off all power when working on air conditioning equipment.
             

Problem # 8: Air conditioner is freezing up

You see frost or ice on the suction line (black insulated line). Any areas that are not insulated are covered with ice. You are not getting hardly any air flow out of your registers. Your evaporator coil is iced up completely. Most of the time this is caused by AC being low on refrigerant charge. There are other causes such as:
1. Dirty air filter or some air flow restriction.
2. Dirty blower
3. Slow or dragging blower motor (might need a new capacitor).
4. Dirty stopped up Evaporator coil (Need to have HVAC tech clean coil)
5. Long Air conditioning runs times. Setting thermostat below 72 degrees with cool outside conditions.
6. A stuck contactor that keeps the outdoor unit running even when the indoor blower is not running or when the thermostat is calling for cooling. Most of the time a freeze up condition is caused by a low refrigerant charge. Since the air conditioning system is supposed to be a leak free, sealed system this means you have a leak somewhere. I would recommend using the Schrader valve caps to make sure that you don’t have a leak in the Schrader valves. These caps have a rubber seal inside of them and insure a leak proof seal.

  
Schrader Caps Installed on an outdoor AC unit.
Schrader caps in box.

What to Check for If Your Air Conditioning System is not working:

1. Check the circuit breaker to make sure the breaker has not tripped. The breaker would probably be a double pole 30, 40 or 50 amp breaker. Even though the breaker looks like it is on I would still flip it all the way to off and back on again just to make sure. Sometimes one leg of a double pole breaker will hold in the other leg and make the breaker appear to look like it is, "ON" when it has actually been tripped.

2. Make sure your thermostat is turned down to a temperature that will allow the air conditioning system to come on. If your thermostat has the little levers on it then it would not hurt to flip the little lever from "OFF" to "COOL”. Sometimes the contacts in the thermostat do not make the connection and flipping the levers will reestablish the connection. I would turn your fan to the "ON" position. Did the fan come on? If the fan did not come on check the switch on the side of your furnace to make sure it has not been turned to "OFF". Make sure your filter access door and furnace door are secure. Many of the furnaces have a switch activated door for your safety. When the door is not completely on the furnace will not operation. This keeps the furnace from coming on when someone is servicing the blower or filter.

3. If your outdoor unit is running listen to determine if the fan is the only thing running or is the compressor running too?

4. Turn off your electrical power to the outdoor unit by pulling the disconnect switch or turn off the indoor circuit breaker. Take the screws off your air conditioner control access panel. Check with a multi-meter to make sure the power is actually off. Touch the top of the compressor. Is the compressor very hot? If the compressor is hot then the compressor could be out on thermal over-load. You need to wait and let the compressor cool down before you test your system again. Use water from a hose and gently let it run over the compressor to cool it down quickly. Sometimes it can take 2 or 3 hours for a compressor to cool down. After it has cooled down reapply power. Did the compressor start? Did the fan start? If the fan did not start with the compressor then this is why the compressor over heated. Check your fan motor and fan run capacitor to make sure the fan blade is free and the capacitor is in good shape. You can check the fan bearings by spinning the blade by hand the blade should continue to spin 3 to 5 seconds after you spin it. If it doesn't then you probably need a new fan motor. Another reason the compressor over heated could be that the system is low on refrigerant. Is the suction line (the line with the black insulation) cold like a cold coke can right out of the refrigerator after the unit runs for 10 to 15 minutes. If it is not cold, then you need to add some refrigerant. The refrigerant is what keeps the compressor running cool. If the system is low on refrigerant then you do not get the cool gas coming back to keep the compressor running cool. The compressor over heats and this will eventually melt the windings down in the compressor and contaminant the whole refrigeration system! This is not good. Eventually the compressor will ground out and you will need a new compressor or new system. Make sure that suction line is cold or you might be low on refrigerant charge. You will need to call a service technician to charge up your system if it is low. Now EPA requires that you be licensed and certified to purchase and use refrigerants.

5. Inspect your wiring to make sure that you do not have any burnt connections. Repair the burnt connections if you have some.

6. Inspect the capacitor/capacitors to see if they are swollen looking. If they are swollen purchase a new capacitor from our capacitor page.

7. Take the compressor terminal cover off and inspect the terminals on the compressor. Sometimes the compressor terminal cover can be a bear to take off. Use a screw driver to release the metal clip that holds the cover on. Sometimes the cover slides off. Sometimes the terminals unplug from the compressor. If any of the compressor terminals are burnt then you could probably use our Term-Lok compressor terminal repair kit to repair the terminals. See Term-Lok compressor terminal repair kit above on this page.

8. Inspect your contactor. Is your contactors points look burnt? You might need to purchase a contactor.

9. When you plug in the disconnect and apply power to your outdoor unit does the fan start and the compressor try to start, but make a "UGGGG" sound. This means the compressor is locked up. The compressor is an electric motor, enclosed in a case, with a piston similar to what you would find in a car. When you hear that "UGGG" sound it is telling you that the piston is locked up. You need to try to unlock the piston. If you can not unlock the piston then you need a new compressor or air conditioning system. You might want to purchase a Super-Boost hard start capacitor. The Super-Boost is also listed above on this page. If you purchase and hook-up the hard start capacitor and the compressor still will not start then you will need a new compressor or system. I say, "System" instead of just outdoor unit because it is recommended that you change both the outdoor unit and the indoor evaporator coil when you install a new system. Manufacturer says that it will damage the outdoor unit if you do not change the evaporator coil too.

How Air Conditioners Work

Air conditioners employ the same operating principles and basic components as your home refrigerator. Refrigerators use energy (usually electricity) to transfer heat from the cool interior of the refrigerator to the relatively warm surroundings of your home; likewise, an air conditioner uses energy to transfer heat from the interior of your home to the relatively warm outside environment.
An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper.
A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.
The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling your home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the outside air flowing over the condenser's metal tubing and fins.
Throughout the second half of the 20th century, nearly all air conditioners used chlorofluorocarbons (CFCs) as their refrigerant, but because these chemicals are damaging to Earth's ozone layer, CFC production stopped in the United States in 1995. Nearly all air conditioning systems now employ halogenated chlorofluorocarbons (HCFCs) as a refrigerant, but these are also being gradually phased out, with most production and importing stopped by 2020 and all production and importing stopped by 2030.
Production and importing of today's main refrigerant for home air conditioners, HCFC-22 (also called R-22), will begin to be phased out in 2010 and will stop entirely by 2020. However, HCFC-22 is expected to be available for many years as it is recovered from old systems that are taken out of service. As these refrigerants are phased out, ozone-safe hydrofluorocarbons (HFCs) are expected to dominate the market, as well as alternative refrigerants such as ammonia.

Maintaining Your Air Conditioner
An air conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air conditioning performance while energy use steadily increases.
Air Conditioner Filters
The most important maintenance task that will ensure the efficiency of your air conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Keeping the filter clean can lower your air conditioner's energy consumption by 5%–15%.
For central air conditioners, filters are generally located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself. Room air conditioners have a filter mounted in the grill that faces into the room.
Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.
Air Conditioner Coils
The air conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil, reducing its ability to absorb heat. To avoid this problem, check your evaporator coil every year and clean it as necessary.
Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins.
You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.
Coil Fins
The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.
Condensate Drains
Occasionally pass a stiff wire through the unit's drain channels. Clogged drain channels prevent a unit from reducing humidity, and the resulting excess moisture may discolor walls or carpet.
Window Seals for Room Air Conditioners
At the start of each cooling season, inspect the seal between the air conditioner and the window frame to ensure it makes contact with the unit's metal case. Moisture can damage this seal, allowing cool air to escape from your house.
Preparing for Winter
In the winter, either cover your room air conditioner or remove and store it. Covering the outdoor unit of a central air conditioner will protect the unit from winter weather and debris.